1. Field of the Invention
The invention relates to a retightener with a pyrotechnical charge for safety-belt automatic wind-up devices having an energy converter, wherein the explosive pressure of the fired charge acts, in the case of danger, on a retightening element which tightens the safety belt around the body of the motor vehicle passenger to be protected.
2. Description of the Prior Art
Retighteners of the type with a pyrotechnic propellant charge serve to eliminate belt looseness, in the case of danger, by pulling back the belt, so that the belt fits the body of the passenger to be protected as closely as possible and the free forward fall up to the point that the belt becomes effective is kept as small as possible.
In one known design of retightener, a piston guided in a tight cylinder with its piston rod engaging the safety belt with its free end, is displaced in the cylinder, in the case of danger, by the explosive pressure of a pyrotechnical charge, and the belt is thereby retightened.
Rotary tighteners which are combined with the automatic wind-up are also known. In such devices the explosive pressure of the pyrotechnic propellant charge drives a turbine wheel which is fastened on the shaft of an automatic wind-up.
The so-called linear tighteners, which work with a piston guided in a cylinder, have the disadvantage that they have only a relatively small retightening travel distance, compared to the relatively large volume they occupy. In order to be effective the linear tighteners must be tightly sealed and this requires a great deal of effort as well as adding materially to the cost.
The effect of the known rotary tighteners in practice was found insufficient to adequately retighten the belt because the pressure of the explosion can be transmitted to the turbine wheel only with low efficiency.